fix(#2190): replace MANAGER_AGENT fallbacks with "operator" for attribution

- loose_ends.rs: NULL submitter on legacy approval rows → "operator"
- questions.rs: NULL submitter on cancel_loose_end → "operator"
- server.rs: HostRequest::RequestSpawn submitter → "operator"
- dashboard.rs: web-UI spawn submitter → "operator"
- socket_server.rs: submit_init_config with no declared parent → "operator"
- mcp.rs: drop MANAGER_AGENT exception from check_send_allowed; keep <parent> only

hive-c0re/src/questions.rs

@@ -203,13 +203,14 @@ pub fn handle_cancel_loose_end(
             // may withdraw it. Without the ownership check, any
             // approvals-group agent could cancel any other's approval by
             // id. A NULL submitter (legacy row predating the column) is
-            // owned by the root agent.
+            // treated as operator-initiated (no agent tracking predates
+            // the column).
             check_can_cancel_approval(canceller)?;
             let submitter = coord
                 .approvals
                 .submitter_of(id)
                 .map_err(|e| format!("{e:#}"))?
-                .unwrap_or_else(|| hive_sh4re::MANAGER_AGENT.to_owned());
+                .unwrap_or_else(|| "operator".to_owned());
             if submitter != canceller {
                 return Err(format!(
                     "cancel_loose_end: approval {id} was submitted by {submitter}, \